I'm not kidding when I say I heard a 2100 player recently remark that to get to 1800 all you need is to not blunder material.
Also Carlsen said of Wesely So a year or two ago that all he really knew were tactics and opening theory.
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In other words, it's all relative. So you have to take what the IM said in context. First, what you actually need is to know is a little bit of everything. After that, sure, you can work a lot on tactics. There should be many ways to get to 2000. Maybe the easiest (after learning a little bit of everything) is tactics.
What is needed to cross 2000 elo ?
At a recent tournament, an IM adviced me that you can beat 2200 elo players bybeing the better tactician. Grab a tactic workbook and work until tactics become your second nature.
People who crossed 2000, or people working to cross 2000, what are your secrets for crossing that mark ?